In a multiple user transmission system, through allocating transmission resources appropriately, data may be transmitted to multiple users simultaneously so as to improve data transmission efficiency. For example, in a Multiple User Multiple Input Multiple Output (MU-MIMO) system, via multiple layers in spatial domain, a base station may serve multiple users simultaneously.
Especially, due to limited spectrum resources, Non-Orthogonal Multiple Access (NOMA) has been more and more focused by people since NOMA is able to greatly improve the spectrum efficiency. The basic idea of NOMA is to perform non-orthogonal transmission at the transmitter, introduce interference intentionally, and detect data by a Sequential Interference Cancellation (SIC) technology at the receiver. Although SIC processing may increase complexity at the receiver, the spectrum efficiency can be greatly improved.